Hi, I believe the behavior you described is just "normal". I have a completely different system and I experience the same. I believe the nVidia developers have more important things to do, like implementing support for the 8900 GT. I think the black window bug is still there, because the driver isn't able to use the system ram. Actually there are systems (like mine) where the this bug shows himself at his worst, meaning I'm getting black windows after the video ram is full. I tried to find out if there are any plans to really solve this problem, but I didn't get any answer .
Good Luck!